content: /*******************************************************************************
   * Copyright 2011, 2012 Chris Banes.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   *******************************************************************************/
  package com.handmark.pulltorefresh.library;
  
  import android.annotation.TargetApi;
  import android.util.Log;
  import android.view.View;
  
  import com.handmark.pulltorefresh.library.PullToRefreshBase.Mode;
  import com.handmark.pulltorefresh.library.PullToRefreshBase.State;
  
  @TargetApi(9)
  public final class OverscrollHelper {
  
  	static final String LOG_TAG = "OverscrollHelper";
  	static final float DEFAULT_OVERSCROLL_SCALE = 1f;
  
  	/**
  	 * Helper method for Overscrolling that encapsulates all of the necessary
  	 * function.
  	 * <p/>
  	 * This should only be used on AdapterView's such as ListView as it just
  	 * calls through to overScrollBy() with the scrollRange = 0. AdapterView's
  	 * do not have a scroll range (i.e. getScrollY() doesn't work).
  	 * 
  	 * @param view - PullToRefreshView that is calling this.
  	 * @param deltaX - Change in X in pixels, passed through from from
  	 *            overScrollBy call
  	 * @param scrollX - Current X scroll value in pixels before applying deltaY,
  	 *            passed through from from overScrollBy call
  	 * @param deltaY - Change in Y in pixels, passed through from from
  	 *            overScrollBy call
  	 * @param scrollY - Current Y scroll value in pixels before applying deltaY,
  	 *            passed through from from overScrollBy call
  	 * @param isTouchEvent - true if this scroll operation is the result of a
  	 *            touch event, passed through from from overScrollBy call
  	 */
  	public static void overScrollBy(final PullToRefreshBase<?> view, final int deltaX, final int scrollX,
  			final int deltaY, final int scrollY, final boolean isTouchEvent) {
  		overScrollBy(view, deltaX, scrollX, deltaY, scrollY, 0, isTouchEvent);
  	}
  
  	/**
  	 * Helper method for Overscrolling that encapsulates all of the necessary
  	 * function. This version of the call is used for Views that need to specify
  	 * a Scroll Range but scroll back to it's edge correctly.
  	 * 
  	 * @param view - PullToRefreshView that is calling this.
  	 * @param deltaX - Change in X in pixels, passed through from from
  	 *            overScrollBy call
  	 * @param scrollX - Current X scroll value in pixels before applying deltaY,
  	 *            passed through from from overScrollBy call
  	 * @param deltaY - Change in Y in pixels, passed through from from
  	 *            overScrollBy call
  	 * @param scrollY - Current Y scroll value in pixels before applying deltaY,
  	 *            passed through from from overScrollBy call
  	 * @param scrollRange - Scroll Range of the View, specifically needed for
  	 *            ScrollView
  	 * @param isTouchEvent - true if this scroll operation is the result of a
  	 *            touch event, passed through from from overScrollBy call
  	 */
  	public static void overScrollBy(final PullToRefreshBase<?> view, final int deltaX, final int scrollX,
  			final int deltaY, final int scrollY, final int scrollRange, final boolean isTouchEvent) {
  		overScrollBy(view, deltaX, scrollX, deltaY, scrollY, scrollRange, 0, DEFAULT_OVERSCROLL_SCALE, isTouchEvent);
  	}
  
  	/**
  	 * Helper method for Overscrolling that encapsulates all of the necessary
  	 * function. This is the advanced version of the call.
  	 * 
  	 * @param view - PullToRefreshView that is calling this.
  	 * @param deltaX - Change in X in pixels, passed through from from
  	 *            overScrollBy call
  	 * @param scrollX - Current X scroll value in pixels before applying deltaY,
  	 *            passed through from from overScrollBy call
  	 * @param deltaY - Change in Y in pixels, passed through from from
  	 *            overScrollBy call
  	 * @param scrollY - Current Y scroll value in pixels before applying deltaY,
  	 *            passed through from from overScrollBy call
  	 * @param scrollRange - Scroll Range of the View, specifically needed for
  	 *            ScrollView
  	 * @param fuzzyThreshold - Threshold for which the values how fuzzy we
  	 *            should treat the other values. Needed for WebView as it
  	 *            doesn't always scroll back to it's edge. 0 = no fuzziness.
  	 * @param scaleFactor - Scale Factor for overscroll amount
  	 * @param isTouchEvent - true if this scroll operation is the result of a
  	 *            touch event, passed through from from overScrollBy call
  	 */
  	public static void overScrollBy(final PullToRefreshBase<?> view, final int deltaX, final int scrollX,
  			final int deltaY, final int scrollY, final int scrollRange, final int fuzzyThreshold,
  			final float scaleFactor, final boolean isTouchEvent) {
  
  		final int deltaValue, currentScrollValue, scrollValue;
  		switch (view.getPullToRefreshScrollDirection()) {
  			case HORIZONTAL:
  				deltaValue = deltaX;
  				scrollValue = scrollX;
  				currentScrollValue = view.getScrollX();
  				break;
  			case VERTICAL:
  			default:
  				deltaValue = deltaY;
  				scrollValue = scrollY;
  				currentScrollValue = view.getScrollY();
  				break;
  		}
  
  		// Check that OverScroll is enabled and that we're not currently
  		// refreshing.
  		if (view.isPullToRefreshOverScrollEnabled() && !view.isRefreshing()) {
  			final Mode mode = view.getMode();
  
  			// Check that Pull-to-Refresh is enabled, and the event isn't from
  			// touch
  			if (mode.permitsPullToRefresh() && !isTouchEvent && deltaValue != 0) {
  				final int newScrollValue = (deltaValue + scrollValue);
  
  				if (PullToRefreshBase.DEBUG) {
  					Log.d(LOG_TAG, "OverScroll. DeltaX: " + deltaX + ", ScrollX: " + scrollX + ", DeltaY: " + deltaY
  							+ ", ScrollY: " + scrollY + ", NewY: " + newScrollValue + ", ScrollRange: " + scrollRange
  							+ ", CurrentScroll: " + currentScrollValue);
  				}
  
  				if (newScrollValue < (0 - fuzzyThreshold)) {
  					// Check the mode supports the overscroll direction, and
  					// then move scroll
  					if (mode.showHeaderLoadingLayout()) {
  						// If we're currently at zero, we're about to start
  						// overscrolling, so change the state
  						if (currentScrollValue == 0) {
  							view.setState(State.OVERSCROLLING);
  						}
  
  						view.setHeaderScroll((int) (scaleFactor * (currentScrollValue + newScrollValue)));
  					}
  				} else if (newScrollValue > (scrollRange + fuzzyThreshold)) {
  					// Check the mode supports the overscroll direction, and
  					// then move scroll
  					if (mode.showFooterLoadingLayout()) {
  						// If we're currently at zero, we're about to start
  						// overscrolling, so change the state
  						if (currentScrollValue == 0) {
  							view.setState(State.OVERSCROLLING);
  						}
  
  						view.setHeaderScroll((int) (scaleFactor * (currentScrollValue + newScrollValue - scrollRange)));
  					}
  				} else if (Math.abs(newScrollValue) <= fuzzyThreshold
  						|| Math.abs(newScrollValue - scrollRange) <= fuzzyThreshold) {
  					// Means we've stopped overscrolling, so scroll back to 0
  					view.setState(State.RESET);
  				}
  			} else if (isTouchEvent && State.OVERSCROLLING == view.getState()) {
  				// This condition means that we were overscrolling from a fling,
  				// but the user has touched the View and is now overscrolling
  				// from touch instead. We need to just reset.
  				view.setState(State.RESET);
  			}
  		}
  	}
  
  	static boolean isAndroidOverScrollEnabled(View view) {
  		return view.getOverScrollMode() != View.OVER_SCROLL_NEVER;
  	}
  }
  